(1) Field of the Invention
This invention generally relates to a rewriteable optical disc, an optical disc recording apparatus, an optical disc recording method, and a storage medium for storing an optical disc recording program, and specifically to a rewriteable optical disc, an optical disc recording apparatus, and an optical disc recording method for facilitating dubbing, and a storage medium for storing an optical disc recording program for facilitating dubbing.
(2) Description of the Prior Art
Recently, DVD(Digital Video/Versatile Disc)-RAM, one of rewriteable optical discs, has been commercialized. The DVD-RAM is a phase-change-type disc having a capacity of several giga bytes. Now that MPEG and MPEG2, standards for compressing/encoding AV (Audio Visual) data, have gone into practical use, it is expected that the DVD-RAM will be used not only in computers but as an AV recording/reproducing medium. That is, the widespread expectation is that the DVD-RAM will be prevalent and replace the magnetic tape which has been a major AV recording/reproducing medium.
It is possible for users to record data onto DVD-RAMs while this is not possible with read-only DVDs (hereinafter referred to as DVD-ROMs). As a result, it is expected that DVD-RAMs provide a wide range of uses.
However, it is not so easy to perform dubbing on conventional optical discs as on the magnetic tapes.
The magnetic tapes have independent areas for recording video tracks and audio tracks. Also, video data and audio data are read/written from/onto the magnetic tapes via respectively independent magnetic heads. Accordingly, it is very easy to perform dubbing of audio data on the magnetic tapes. In case of analog video tape recorders, the time (delay) taken for starting reproducing audio or video data read from the magnetic tape via the head is nearly zero. This is the same for the time (delay) taken for starting writing input audio or video data onto the magnetic tape via the head. As a result, data can be recorded onto the magnetic tape at the same time as the data having been recorded on the magnetic tape is reproduced.
In contrast, in case of an optical disc, the video stream and audio stream are multiplexed into one MPEG stream to be recorded onto the disc. Also, only one pickup is used for both reading and writing data from/onto the optical disc. In the MPEG stream, the video stream is placed before and is processed earlier than the audio stream. This is because the amount of video data to be decoded is greater than that of audio data. Such data structure of the MPEG stream and the construction of the recording/reproducing apparatus make it difficult to perform dubbing to record dubbed data onto the optical disc.